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Fractions: Computations


Fractions: Computations & Operations Teaching for Conceptual Understanding Introduction Represent the following operation using each of the representations: Describe ... – PowerPoint PPT presentation

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Title: Fractions: Computations

Fractions Computations Operations
  • Teaching for Conceptual Understanding

  • Represent the following operation using each of
    the representations
  • Describe what the solution means in terms of each
    representation you use.
  • Pictures
  • Manipulatives
  • Real World Situations
  • Symbolic
  • Oral/Written Language

Fractional Parts Counting
5 Fourths
3 Fourths
10 Fourths
10 Twelfths
  • What does the bottom number in a fraction tell
  • What does the top number in a fraction tell us?

Misleading notion of fractions Top number tells
how many. Bottom number tells how many parts
to make a whole.
For example
  • If a pizza is cut in 12 pieces, 2 pieces makes
    1/6 of the pizza
  • Here, the bottom number does not tell us how many
    parts make up the whole!
  • Better Idea!
  • We can assume the top number counts while the
    bottom number tells what is being counted.
  • ¾ is a count of three things called fourths

Using this notion, what is another way to
say/write Thirteen sixths? Explain your rationale.
  • Using the manipulatives, your task is to find a
    single fraction that names the same amount as
  • must be able to provide an explanation for your
  • Then, determine the mixed number for 17/4 and
    provide a justification for your result.

Parts Whole Tasks
If 12 counters are ¾ of a set, how many counters
are in the full set?
If 10 counters are five-halves of a set, how many
counters are in one set? (What must be half of
one set?)
If purple is 1/3, what strip is the whole? If
dark green is 2/3, what strip is the whole? If
yellow is 5/4, what strip is 1 whole?
Dark Green
Dark Green
If the dark green is the whole, what fraction is
the yellow strip?
Dark Green
If the dark green strip is one whole, what
fraction is the blue strip?
Getting to Conceptual Understanding
  • A father has left his three sons 35 camels to
    divide among them in this way
  • One-half to one brother, one-third to another
    brother, and one-ninth to the third brother.
  • How many camels does each brother receive?
    Explain your solution to this problem.

Benchmarks of Zero, One-Half, and One
Sort the following fractions into three groups
close to zero, close to ½, and close to one.
Provide rationale and explanation for your
Close Fractions Name a fraction that is close to
one but not more than one. Name another fraction
that is even closer to one. Explain why you
believe this fraction is even closer to one than
the first. Show using manipulatives.
Partner/ Group Activity
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Exploring Ordering Fractions lt or gt
  • Task Which fraction in each pair is greater?
    Give an explanation for why you think so?
  • What are some of the usual approaches that
    students would choose to use in this activity?
    Why do you think this is?

Conceptual Thought Patterns
  • More of the same size parts to compare 3/8 and
  • - students will choose 5/8 as larger because 5gt3
    right choice, wrong reason
  • - comparing 3/8 and 5/8 should be like comparing
    3 apples and 5 apples

  • Same number of parts, but parts of different
  • to compare ¾ and 3/7
  • Misconception students will choose 3/7 as the
    larger because 7 is more than 4 and the top
    numbers are the same
  • However, if a whole is divided into 7 parts, the
    parts will be smaller than if divided into only 4
    parts thus, ¾ is larger
  • Like comparing 3 apples with 3 melons same
    number of things but melons are bigger

  • More or less than one-half or one whole
  • comparing 3/7 and 5/8
  • 3/7 is less than half of the number of sevenths
    needed to make a whole, so 3/7 is less than
  • thus, 5/8 is more than one-half and is therefore
    the larger fraction

  • Distance from one-half or one whole
  • compare 9/10 and ¾
  • Misconception 9/10 is bigger because 9 and 10
    are the bigger numbers
  • 9/10 is larger than ¾ because although each is
    one fractional part away from a whole, tenths are
    smaller than fourths and so 9/10 is closer to one

Addition and Subtraction Explorations
  • Paul and his brother were each eating the same
    kind of candy bar. Paul had ¾ of his candy bar.
    His brother had 7/8 of a candy bar. How much
    candy did the two boys have together?
  • Using drawings /or manipulatives, solve this
    problem without setting it up in the usual manner
    and finding common denominators?
  • Can you think of two different methods?

One possible Solution
We could take a fourth from the 7/8 and add it to
the ¾ to make a whole. That would leave 5/8.
Thus, the total eaten would be 1 5/8 of candy bar.
Using Cuisenaire Rods for Fraction Computation
  • Jack and Jill ordered two identical sized pizzas,
    one cheese and one pepperoni. Jack ate 5/6 of a
    pizza and Jill ate ½ of a pizza. How much pizza
    did they eat together?
  • What would we expect our students to show that
    would demonstrate their conceptual understanding?

  • Find a strip for the whole that allows both
    fractions to be modeled.

Dark Green
Light Green
Dark Green
Light Green
A Red is 1/3 of the Dark Green, so the solution
is 1 1/3.
Multiplication of Fractions Beginning Concepts
  • Using visual representations/manipulatives, model
    the following computation
  • There are 15 cars in Michaels toy car
    collection. Two-thirds of the cars are red. How
    many red cars does Michael have?

  • Using visual representations/manipulatives, now
    model these following problems
  • You have ¾ of a pizza left. If you give 1/3 of
    the left-over pizza to your brother, how much of
    the whole pizza will your brother get?
  • Someone ate 1/10 of the cake, leaving only 9/10.
    If you eat 2/3 of the cake that is left, how much
    of the whole cake have you eaten?
  • Gloria used 2 ½ tubes of blue paint to paint the
    sky in her picture. Each tube holds 4/5 ounce of
    paint. How many ounces of blue paint did Gloria

When pieces must be subdivided into smaller unit
parts, the problems become more challenging
  • Zack had 2/3 of the lawn left to cut. After lunch
    he cut ¾ of the grass that he had left. How much
    of the whole lawn did he cut after lunch?
  • Bill drank 1/5 of his pop before lunch. After
    lunch he drank 2/3 of what was left. How much pop
    did he drink after lunch?

Division of Fractions Beginning Concepts
  • Think about the following problem
  • Cassie has 5 ¼ yards of ribbon to make three
    bows for birthday packages. How much ribbon
    should she use for each bow if she wants to use
    the same length of ribbon for each?
  • What types of solutions would we anticipate our
    students to come up with?
  • How could we model the solution using
    manipulatives/multiple representations?
  • How many different ways?

  • In the following problem, the parts must be split
    into smaller parts
  • Mark has 1 ¼ hours to finish his three
    household chores. If he divides his time evenly,
    how many hours can he give to each?

  • Inverse vs. Reciprocal
  • 4/5 - representations
  • Think of the many forms that even the symbolic
    can be represented decimals, rates, ratios,
  • Other? More???

  • Applying this Reasoning
  • Solving Problems

  • A A student is sorting into stacks a room full
    of food donated by the school for the local food
    bank. He sorted of it before lunch and then
    sorted of the remainder before school ended.
    What part (fraction) of all the food will be left
    for him to sort after school?

1 3
3 4
  • B Use manipulatives to solve this problem.
    Mark ate half of the candies in a bag. Leila ate
    2/3 of what was left. Now there are 11 candies in
    the bag. How many were in the bag at the start?
  • C Bills Snow Plow can plow the snow off the
    schools parking lot in 4 hours. Janes plowing
    company can plow the same parking lot in just 3
    hours. How long would it take Bill and Jane to
    plow the schools parking lot together?

Think of the math content involved with this
problem Think of some Before activities that
could be used. What would the debrief look/sound
like in the classroom after the task was complete?
Teaching Through Problem Solving
  • D Mrs. Get Fit teaches Math and Phys-ed. To
    incorporate Math into the Phys-ed class, she
    divided the class into eight groups. There are
    three students in each group. The first person in
    the group runs ¼ of a lap of the track, the
    second person runs 1/6 of the track, and the
    third person runs 1/3 of a lap of the track. How
    many laps of the track are run in total by all
    eight teams combined?